High Current, Low Equivalent Series Resistance Printed Circuit Board Coil for Power Transfer Application

ABSTRACT

A method for fabricating an electric coil on a circuit board comprising fabricating on the circuit board a first coil layer comprising a coil trace and a plurality of vias distributed along the length of the coil trace, and overlaying a second coil layer on the first coil layer, wherein the vias of the first coil layer join the first coil layer and the second coil layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/600,969 filed Feb. 20, 2012 by Jorge Zabaco andentitled “Clever Implementation of Wireless Charging Coil Using StandardPrinted Circuit Board Technology,” which is incorporated herein byreference as if reproduced in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

An electric coil (or simply a “coil”) is formed by winding a conductor(usually an insulated solid copper wire) around a non-conductive core tocreate an inductor. One loop of wire is referred to as a turn, and acoil consists of one or more turns. In electronic circuits, electricalconnection terminals referred to as taps are connected to a coil. Acompleted coil assembly with taps is often called a winding. Coils areused in different applications, such as in power transformers andelectromagnets. Coils are also used in inductive charging and resonantinductive coupling applications, where energy is transferred between twoobjects through inductive coupling, e.g., without a conducting mediumbetween the two objects. In inductive charging, there is a relativelysmall gap between two coils, which are located on the sender andreceiver sides of the energy, e.g., within two respective devices.Inductive charging is considered a short-distance “wireless” energytransfer, since charging is achieved without using wires between the twodevices. For example, inductive charging applications include wirelessbattery charging devices. Resonant inductive coupling is the near fieldwireless transmission of electrical energy between two coils that aretuned to resonate at the same frequency. Resonant inductive couplingapplications can achieve longer energy transfer distances than inductivecharging applications. For example, resonant inductive couplingapplications include near-field wireless communications, such asradio-frequency identification (RFID) devices.

SUMMARY

In an embodiment, the disclosure includes a method for fabricating anelectric coil on a circuit board comprising fabricating on the circuitboard a first coil layer comprising a coil trace and a plurality of viasdistributed along the length of the coil trace, and overlaying a secondcoil layer on the first coil layer, wherein the vias of the first coillayer join the first coil layer and the second coil layer.

In another embodiment, the disclosure includes a method for reducing anoverall thickness of a multilayer coil for wireless electrical powertransfer, comprising fabricating a first coil layer comprising a firstwinding trace, overlaying and distributing a plurality of vias acrossthe first coil layer, and overlaying on the vias a second coil layercomprising a second winding trace substantially similar to the windingtrace, wherein the spaces between the vias are determined to increasethe vias coverage of the surfaces of the first coil layer and the secondcoil layer.

In yet another embodiment, the disclosure includes an apparatus for amultilayer PCB coil, comprising a first coil layer of a PCB, a pluralityof vias coupled to and distributed to cover substantially the surface ofthe first coil layer within the PCB, and a second coil layer of the PCBand coupled to the vias to cover substantially the surface of the secondcoil layer, wherein the vias are positioned between the first coil layerand the second coil layer and enable substantially high current and lowequivalent series resistance (ESR) for the multilayer PCB coil.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a top view of a first coil layer of the multicore design.

FIG. 2 is a top view of a second coil layer of the multicore design.

FIG. 3 is a cross sectional view of an embodiment of a multicore designof FIG. 2 taken along line 3-3.

FIG. 4 is a flowchart of an embodiment of a multilayer coil fabricationmethod.

FIG. 5 is a flowchart of another embodiment of a multilayer coilfabrication method.

FIG. 6 is a schematic diagram of an embodiment of a handheld devicecomprising a multilayer coil design.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Wireless charging coils that are used in wireless charging componentsmay require relatively high current capabilities and relatively low ESR.The high current and low ESR increases power transfer efficiency of thecoil. For example, wireless charging coils may be used in inductivecharging components for mobile devices (e.g., smartphones) and mobilecomputers (e.g., laptops and tablets). To meet such requirements, thestandard method to fabricate such coils may be based on using andsoldering electric or conductive wires onto electric circuit boards ofthe devices. However, using electric wires to construct charging coilsmay have limits on the current capability and low ESR resistance thatmay be achieved, e.g., due to the dimensions and materials involved. Forexample, to achieve the required high current capabilities andrelatively low ESR resistance for wireless (or inductive) charging,coils made out of wires may require a minimum thickness that may not besuitable for some mobile or handheld devices, such as relatively flat(thinner) smartphones and tablets. A more promising coil design toincrease current capability and reduce ESR may be based on integratedcircuit fabrication methods, such as using PCB technology and relatedfabrication processes. Such charging coils may be used in relativelyflat mobile devices that have limits on device thickness. The PCB may bea non-conductive substrate that mechanically supports and electricallyconnects electronic or electrical components using conductive pathways,tracks, or traces, e.g., that may be etched from copper sheets laminatedonto the substrate. The PCB may also be coated for protecting thecomponents, e.g., using wax, silicone rubber, polyurethane, acrylic, orepoxy.

Disclosed herein is a fabrication method and apparatus for a multilayercoil design. The method may comprise fabricating multiple coil layers ona PCB and joining the coil layers together using a plurality of vias.The vias may be any structures/material used as vertical electricalconnections between different layers of conductors in a physicalelectronic circuit. The electric coil design may be used for wirelesscharging application and the method may use PCB technology andfabrication processes. The method may enable and facilitate fabricationof thinner coil layers on a PCB, where the coil traces may be fabricatedusing available circuit fabrication processes and may be made thinnerthan typical electric wires. This may also allow the integration of thecoil design with other circuit components of a device. The vias thatjoin or link the coil layers may be distributed along the length of thetraces of the coil layers to enhance the current capability and lowerthe ESR of the entire coil design (the multilayer coil), and henceobtain an effective wireless charging coil. The high current and low ESRcoil may also be suitable for near-field wireless antenna designs. Forexample, the coil may be a component of a near-field wireless antennadesign in a RFID device. The method and apparatus may also be used inother coil applications or devices that require efficient power transferand relatively thin design, e.g., since the multilayer coil may beintegrated with other circuit components and hence allow a more compactdesign.

The thinner multilayer coil design may be suitable for portable devices,such smartphones, tablets, and laptops that have thinner designs. Thecoil fabrication method may have reduced cost since PCB technology ismature and has lower cost in comparison to other fabricationtechnologies, for example in comparison to constructing coil wires andthen soldering the coil wires to a PCB comprising wireless chargingcircuitry. The electric coil design may also be easier to manufactureusing PCB technology, where a single PCB may be needed. Using a singlePCB may also eliminate the need to solder the coil to another PCBcomprising the wireless charging circuitry. Further, using a singleboard, where the coil and the circuitry may be integrated duringfabrication, may be more reliable than having the two components (thecoil and the wireless charging circuitry) soldered to one another.

FIGS. 1-3 illustrate an embodiment of a multilayer coil design 100,which may be fabricated using PCB technology. The multilayer coil design100 may comprise a plurality of coil layers fabricated on a PCB 190. ThePCB 190 may be a non-conductive or semiconductor substrate, e.g., asilicon board. The number of coil layers may be determined such that toachieve the required current capability and ESR for the coilapplication. To achieve relatively high current capabilities andrelatively low ESR for wireless charging or near-field communicationapplications, multiple coil layers may be fabricated and overlaid usingPCB technology and fabrication processes. The coil layers may comprise afirst coil layer 102 positioned on top of the PCB 190 and a second coillayer 104 overlaid on the first coil layer 102. FIG. 1 illustrates a topview of the first coil layer 102 and FIG. 3 shows a top view of thesecond coil layer 104. FIG. 3 shows a cross sectional view of themultilayer coil design 100 taken along line 3-3 of FIG. 2. Themultilayer coil design 100 may also comprise a plurality of vias 108positioned between the first coil layer 102 and the second coil layer104. The first coil layer 102, the second coil layer 104, and the vias108 may be fabricated using lithography, etching, and depositionprocesses in any suitable combination.

The first coil layer 102, the second coil layer 104, and optionally anyadditional number of overlaid layers, which may have substantiallysimilar patterns, may be combined on the PCB 190 into a coil design thatachieves a required current capability and ESR for an intendedapplication, e.g., a wireless charging or near-field communicationsdevice or component. The first coil layer 102 and the second coil layer104 may have a substantially similar pattern that includes a windingtrace 106. The winding traces of the coil layers may be shaped in a coilpattern. Other suitable patterns that have a winding or coil pattern mayalso be used. A coil pattern (or a winding trace pattern) may bedesigned in a first layer, e.g., the first coil layer 102, and thencopied or mirrored to a second overlaid layer, e.g., the second coillayer 104, or as many additional overlaid layers as needed to meetcurrent, ESR, and/or impedance required for the wireless charging ornear-field communication application. Other design criteria may also bemet using the fabrication method and the coil layers design, such asdimension criteria and/or other electric properties requirements. Thecoil layers may be overlaid (on the same PCB) and combined to form acoil design or a final coil structure that meets the required criteria.For instance, increasing the number of layers may increase the powertransfer capability of the multilayer coil design 100. The number anddimensions of the multilayer coil may also be determined to meet athickness (height of coil layers) requirement for thin portable devices(e.g., smartphones or tablets).

Specifically, to increase current and reduce ESR in the multilayer coildesign 100, the coil layers may be joined or otherwise electricallyconnected using the vias 108, which may be distributed throughout thecoil pattern. The vias 108 may have cylindrical or other suitableshapes, which may be vertical with respect to the coil layers (as shownin FIG. 1), extend between adjacent coil layers, and connect the facingsurfaces (the traces 106) of the adjacent coil layers. For instance, thevias 108 may be shaped as solid circles distributed to coversubstantially the coil pattern (trace 106) of the first coil layer 102,as shown in FIG. 2. A plurality of additional vias 108 may similarly bedistributed across the trace 106 of the second coil layer 104 (as shownin FIG. 3), for instance if a third coil layer (not shown) is overlaidon the second coil layer 104 to connect the second coil layer 104 andthe third coil layer. The vias 108 may comprise conducting material thatjoins (electrically) the different coil layers with each other andallows current to flow throughout the multiple coil layers. Forinstance, the vias 108 may be composed of the same material of thetraces of the coil layers. Increasing the number of vias 108 anddistributing the vias 108 substantially entirely across two adjacentcoil surfaces may increase the current flow between the two adjacentcoil traces 106 and hence reduce ESR for the multilayer coil design 100,e.g., in comparison to distributing fewer vias at some portions of thecoil surfaces.

Further, the relatively thin coil pattern at each layer may reduce theoverall series resistance (the ESR) of the multilayer coil design 100.For example, a coil design comprising two coil layers with traces ofabout 25 micrometers thickness may have an overall series resistance ofabout 0.35 ohms or less. The coil traces or layers may have about thesame thickness, which may be determined to meet a desired ESR for themultilayer coil design 100. Using multiple layers of coil, which arecoupled to each other using the vias 108, may also reduce the width ofthe multilayer coil design 100, since the coil conducting material(trace material) may be layered in height (along the thickness of thePCB) to occupy a smaller area and achieve about the same inductiveproperty. For example, overlaying a plurality of substantially similarcoil traces reduces the overall width of the coil traces in the PCBlayers in comparison to fabricating only one coil trace that hassubstantially the same thickness of one of the overlaid coil traces. Thereduced overall width of the coil design may allow using the multilayercoil structure in compact devises, such as handheld devices.

The coil traces 106 and the vias 108 may be aligned properly, e.g.,during fabrication, to ensure proper joining of the multiple coillayers. The coil layers may be fabricated and overlaid on the same boardusing PCB technology and fabrication processes that may be repeated asnecessary to construct each layer. Each layer may comprise a coilpatterned obtained using traces (e.g., instead of soldiering wires). Thetraces 106 may comprise electrically one or more conductive materials,such as copper, gold, aluminum, silver, other conductors, orcombinations thereof and may be surrounded by non-conductive materialsuch as any dielectric material suitable for PCB fabrication. Themultiple layers may also be integrated or overplayed with other circuitcomponents 180 (e.g., charging or wireless transmission circuitrycomponents) on the same board. The other circuit components 180 may befabricated between or adjacent to the coil layers on the PCB 190.

In one scenario of the fabrication process, a dielectric may be firstdeposited or sputtered on the PCB 190. For each layer, the trace 106 maybe patterned and then etched. The etched patterns may then be filledwith electrically conducting material using deposition. The coil layersmay be fabricated in similar manner, e.g., using the same patterns, andoverlaid accordingly to obtain an overlay of coil patterns (traces 106).The vias 108 between two coil layers may be fabricated via deposition,patterning, etching, and optionally other necessary processes as part ofthe fabrication step of one of the coil layers (e.g., the bottom coillayer), during the fabrication steps of the two adjacent coil layers, asa separate fabrication step from the coil layers, or combinationsthereof. For instance, the vias 108 may be fabricated by patterning thevias 108 on the traces 106 using lithography and then etching.Deposition may be achieved using any vacuum deposition procedures ortechnologies. The trace 106 may be patterned using lithography (e.g.,photolithography, electronic beam lithography, or other lithographytechnology) or other suitable circuit patterning means (e.g.,imprinting). The patterned structure may be etched, e.g., using chemicaletching, gas etching, plasma, or other suitable means. The other circuitcomponents 180 may also be fabricated on the PCB 190 and integrated withthe coil design or structure.

FIG. 4 illustrates an embodiment of a multilayer coil fabrication method400 for obtaining a relatively thin coil design with high current andlow ESR, such as the multilayer coil design 100, using PCB technology.At block 402, a coil layer may be fabricated comprising a plurality ofvias distributed along the length of the coil layer and/or cover asubstantial portion of the surface of the coil layer, e.g., the coiltrace. The vias may be distributed across the coil pattern or traces andmay be positioned to optimize or improve current flow and seriesresistance. For instance, increasing the number of vias on the coilsurface and distributing or arranging the vias proportionally or evenlyacross the entire surface may increase current flow and reduceresistance at the coil layer. The vias may be distributed along thelength of the coil trace to cover about the entire surface except forthe spaces between the vias. The spaces between the vias may be arrangedto be as small as allowed by the fabrication process to increase thesurface coverage of the coil trace by the vias. In an embodiment, theindividual vias may have about the same size, surface, and/ordimensions, which may determine the quantity of vias that cover thesurface of the coil trace. For example, increasing the surface of theindividual vias may reduce the total number of vias on the surface ofthe coil trace. Alternatively, reducing the surface of the individualvias may increase the total number of vias on the surface of the coiltrace. In another embodiment, at least some of the vias may havedifferent sizes and surfaces to optimize or increase current flow andseries resistance.

At block 404 an additional coil layer may be overlaid on the coil layersuch that the vias of the coil layer join (connect) the coil layer andthe additional coil layer. The additional coil layer pattern (or trace)may be substantially similar to the coil layer pattern and the two coillayers may be overlaid to overlap completely or substantially. Theadditional coil layer may also comprise a plurality of additional viasthat may join the additional coil layer to the coil layer, the vias ofthe coil layer, or to additional overlaid coil layers. The blocks 402and 404 may be repeated (indicated by the dashed line arrows in FIG. 4)as needed to establish as many coil layers required to meet the currentcapabilities and series resistance for the entire coil design.

FIG. 5 illustrates an embodiment of another multilayer coil fabricationmethod 500 for obtaining a relatively thin coil design with high currentand low ESR, such as the multilayer coil design 100. The method 500 maybegin at block 502, where a first coil layer comprising a first windingtrace may be fabricated, e.g., on a PCB, any other circuit board, asilicon substrate, or a silicon/semiconductor wafer. At block 504, aplurality of vias may be overlaid and distributed across the first coillayer. The vias may be distributed to cover substantially the tracesurface along the length of the entire winding trace. At block 506,second coil layer comprising a second winding trace substantiallysimilar to the winding trace may be overlaid on the vias. As such, thevias may couple or join the second coil layer to the first coil layer.

At bock 508, the method 500 may determine whether more coil layers areneeded to meet coil design requirements, such as current, resistance,thickness, size, and/or other electrical and physical properties. Ifmore coil layers are needed, the method 500 may proceed to block 510.Otherwise, the method 500 may end. At block 510, a plurality ofadditional vias may be overlaid and distributed across the last overlaidcoil layer, e.g., the second coil layer. The additional vias may bedistributed on the second winding trace substantially similar to thevias across the first winding trace. In some scenarios, the firstwinding trace and the second winding trace may be distributeddifferently across the corresponding surface (coil layers) to optimizecurrent flow and/or ESR for the entire multilayer coil design. At block512, an additional coil layer comprising an additional winding tracesubstantially similar to the winding trace may be overlaid on theadditional vias. As such, the additional vias may couple or join theadditional coil layer to the previously fabricated and overlaid coillayers to achieve a multilayer coil design with the desired properties.

FIG. 6. is a schematic diagram of an embodiment of a handheld device 600that may comprise a multilayer coil design, e.g., the multilayer coildesign 100. The handheld device 600 may be a smartphone that comprises awireless charging component (not shown), e.g., a wireless chargingcircuit that includes the multilayer coil design and may be used forcharging a battery (not shown) of the smartphone. For example, thehandheld device 600 may be positioned near a charging station comprisingan inductive charging coil, thereby charging the handheld device 600.The smartphone may be a relatively thin smartphone (in comparison tosmartphone device standards), e.g., may have a thickness of less thanabout one centimeter. The smartphone may be configured for wirelessdata/voice communications using cellular networks, Wireless Fidelity(WiFi) networks, or both. In some embodiments, the smartphone may alsocomprise a near-field component, e.g., a radio-frequency identificationdevice that may also include a multilayer coil design.

The handheld device 600 may comprise a housing 601, a microphone 612, atouchscreen 614, a speaker 616, a front (face) camera 619, one or morevolume control buttons 650, and one or more device function buttons 660.The housing 601 may be a casing that forms the external surface of thehandheld device 600 and provides protection to the internal componentsof the handheld device 600, including the wireless charging component, abattery, antenna circuits, and other electronic components. The housing601 may be a non-conductive casing, such as a plastic casing. Themicrophone 612 may comprise one or more slots in the housing 601, whichmay be coupled to a microphone circuit under the housing 601. Thetouchscreen 614 may be configured to display text, video, and graphicsand to receive input from a user by tapping on or touching thetouchscreen 614 on a corresponding point (e.g., a text or graphic). Thespeaker 616 may comprise one or more slots (e.g., circular or otherwiseshaped slots) in the housing 601, which may be coupled to a speakercircuit under the housing 601. The front (face) camera 619 may bepositioned inside a slot in the housing 601 and may comprise a one ormore optical components (e.g., one or more lenses) coupled to a digitalvideo processing circuit inside the housing 601. The volume controlbuttons 650 may be configured to adjust the volume of the speaker,including increasing, decreasing, and muting the volume. The devicefunction buttons 660 may comprise a plurality of buttons forimplementing different functions, such as a home menu button, a returnbutton, a phone list button, a power button, a lock button, and/or otherdevice function buttons.

In some embodiments, the handheld device 600 may comprise an externalantenna, such as a metal strip positioned around the sides of thehousing 601. The handheld device 600 may also comprise other externalcomponents (not shown), such as a rear camera, one or more connectionslots for connecting a power cord, a data transfer cord (e.g., auniversal serial bus (USB) cable), or a portable memory card, orcombinations thereof. At least some of the different internal circuitsand components of the handheld device 600 may be fabricated on the samecircuit board, e.g., a PCB. The components above of the handheld device600 may be shaped, arranged, and positioned as shown in FIG. 6 or in anysuitable form or design.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R₁, and an upper limit,R_(u), is disclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is a variableranging from 1 percent to 100 percent with a 1 percent increment, i.e.,k is 1 percent, 2 percent, 3 percent, 4 percent, 7 percent, . . . , 70percent, 71 percent, 72 percent, . . . , 96 percent, 97 percent, 98percent, 99 percent, or 100 percent. Moreover, any numerical rangedefined by two R numbers as defined in the above is also specificallydisclosed. The use of the term about means±10% of the subsequent number,unless otherwise stated. Use of the term “optionally” with respect toany element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as comprises,includes, and having should be understood to provide support fornarrower terms such as consisting of, consisting essentially of, andcomprised substantially of. Accordingly, the scope of protection is notlimited by the description set out above but is defined by the claimsthat follow, that scope including all equivalents of the subject matterof the claims. Each and every claim is incorporated as furtherdisclosure into the specification and the claims are embodiment(s) ofthe present disclosure. The discussion of a reference in the disclosureis not an admission that it is prior art, especially any reference thathas a publication date after the priority date of this application. Thedisclosure of all patents, patent applications, and publications citedin the disclosure are hereby incorporated by reference, to the extentthat they provide exemplary, procedural, or other details supplementaryto the disclosure.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method for fabricating an electric coil on acircuit board comprising: fabricating on the circuit board a first coillayer comprising a coil trace and a plurality of vias distributed alongthe length of the coil trace; and overlaying a second coil layer on thefirst coil layer, wherein the vias of the first coil layer join thefirst coil layer and the second coil layer.
 2. The method of claim 1,wherein the vias are distributed substantially across the entire coiltrace to achieve higher current capability, lower equivalent seriesresistance (ESR), or both for the electric coil.
 3. The method of claim1, wherein the first coil layer and the second coil layer are overlaidon the circuit board, and wherein additional circuit components areintegrated, overlaid, or both with the first coil layer and the secondcoil layer on the circuit board.
 4. The method of claim 1, wherein thesecond coil layer comprises a second coil trace and a plurality ofsecond vias.
 5. The method of claim 4, wherein the second vias join thesecond coil trace to the coil trace, the vias, or both.
 6. The method ofclaim 4 further comprising overlaying a third coil layer on the secondcoil layer, wherein the second vias of the second coil layer join thesecond coil layer and the third coil layer.
 7. The method of claim 4,wherein the second coil trace mirrors the coil trace.
 8. The method ofclaim 1 further comprising overlaying one or more additional coil layerson the first coil layer and the second coil layer to meet currentcapability, equivalent series resistance (ESR), or both requirements forthe electric coil.
 9. A method for reducing an overall thickness of amultilayer coil for wireless electrical power transfer, comprising:fabricating a first coil layer comprising a first winding trace;overlaying and distributing a plurality of vias across the first coillayer; and overlaying on the vias a second coil layer comprising asecond winding trace substantially similar to the winding trace, whereinthe spaces between the vias are determined to increase the vias coverageof the surfaces of the first coil layer and the second coil layer. 10.The method of claim 9, wherein the vias between the first coil layer andthe second coil layer are distributed substantially evenly across thesurfaces of the first coil layer and the second coil layer.
 11. Themethod of claim 9 further comprising: overlaying and distributing aplurality of second vias across the second coil layer and overlaying onthe second vias a third coil layer comprising a third winding tracesubstantially similar to the winding trace, wherein the spaces betweenthe second vias are reduced to increase the second vias coverage of thesurfaces of the second coil layer and the third coil layer.
 12. Themethod of claim 11, wherein the vias between the first coil layer andthe second coil layer and the second vias between the second coil layerand the third coil layer are distributed similarly or differently toincrease overall current flow and series resistance in the multilayercoil.
 13. The method of claim 9, wherein the vias are overlaid acrosssubstantially the entire surfaces of the first coil layer and the secondcoil layer to increase current flow between the first coil layer and thesecond coil layer, reduce equivalent series resistance (ESR), andincrease power transfer in comparison to overlaying fewer vias at someportions of the surfaces of the first coil layer and the second coillayer.
 14. The method of claim 9, wherein the first coil layer and thesecond coil layer have a thickness determined to meet a desiredequivalent series resistance (ESR) for the multilayer coil and to allowusing the multilayer coil for a wireless charging component in arelatively thin handheld device.
 15. The method of claim 9, wherein thevias are fabricated by patterning the vias on the first coil layer usinglithography and then etching.
 16. The method of claim 9, wherein thespaces between the vias are reduced as much as allowed by the PCBfabrication to increase the surface coverage of the first coil layer andthe second coil layer by the vias.
 17. The method of claim 9, whereinthe vias have about the same size, surface, and dimensions that aredesigned to determine a quantity of vias that cover the surfaces of thefirst coil layer and the second coil layer.
 18. The method of claim 9,wherein at least some of the vias have different sizes that aredetermined to increase current flow and series resistance in themultilayer coil.
 19. An apparatus for a multilayer printed circuit board(PCB) coil, comprising: a first coil layer of a PCB; a plurality of viascoupled to and distributed to cover substantially the surface of thefirst coil layer within the PCB; and a second coil layer of the PCB andcoupled to the vias to cover substantially the surface of the secondcoil layer, wherein the vias are positioned between the first coil layerand the second coil layer and enable substantially high current and lowequivalent series resistance (ESR) for the multilayer PCB coil.
 20. Theapparatus of claim 19 further comprising one or more other circuitcomponents integrated with the first coil layer and the second coillayer on the PCB.
 21. The apparatus of claim 19, wherein the multilayerPCB coil is a component used in a wireless charging device.
 22. Theapparatus of claim 19, wherein the multilayer PCB coil is a componentused in a near-field transmission device.
 23. The apparatus of claim 19,wherein the vias have a cylindrical shape and are vertical with respectto the surfaces of the first coil layer and the second coil layer.